C#の「VBのMyClass」にあたるキーワードは？

class Person {
    private DateTime birthday;

    public int Age {
        get {
            int age = DateTime.Now.Year - this.BirthDay.Year;
            if (DateTime.Now.DayOfYear < this.BirthDay.DayOfYear) age--;
            if (age < 0) thow new ApplicationException("生まれてないよ！？");
            return age;
        }
    }

    public virtual bool CanDrink {
        get {
            return (this.Age >= 20);
        }
    };
}

class Employee : Person {
    public int 数え年 {
        get {
            return DateTime.Now.Year - this.BirthDay.Year;
        }
    }
}

class ひね坊 : Person {
    public new int Age {
        get {
            return DateTime.Now.Year - this.BirthDay.Year;
        }
    }
}

    if (emp.Age >= 20) {
        if (emp.CanDrink) {
            return @"飲めや歌えの大騒ぎ";
        } else {
            return @"俺の酒が飲めねぇってか、おらぁ！";
        }
    } else {
        return @"未成年は、しゃぁないわな";
    }